Oracle Database is nothing but collection of important files(C R D
files).
1.Control files
2.Redo Log files
3.Data files
The minimum number of data files that are required to create a database
are 2.
1.system.dbf
2.sysaux.dbf
In 10g version of oracle, oracle has introduced sysaux.dbf.
The minimum number of online Redo Log groups that are required to create
a database are 2.
e.g : redo1a.log, redo1b.log
the minimum number of control files that are required to create a
database is 1.
e.g : control01.ctl
All the 3 physical files of the database are binary in nature and not
recommended to edit them either with vi editor or notepad.
In version 9i, the minimum size size of online redo log file is 64K
where as from 10g it is 4MB.
Every data file will have its own header which contains information
related to the data file
SCN(System Sequence Number)
Log Sequence Number
CheckPoint Change Number
Absolute File Number
Relative File Number
Absolute File Number uniquely identifies the data file within the
database.
Relative File Number uniquely identifies the data file within the
TableSpace.
For every 3 seconds, oracle generates one number(SCN) and updates to the
data file header as well as Control file.
Whenever we issue startup/shutdown oracle generates SCN and it will be
updated to the data file header as well as Control file.
